1. Field of the Invention
The present invention relates to a method and apparatus for impacting a, surface with a controlled desired impact energy. More particularly, the present invention relates to a method and apparatus for impacting a surface with a small desired and controllable impact energy, whereby the sensitivity of impact detectors mounted on the surface, and in particular a surface of a nuclear reactor coolant system, can be tested.
2. Description of the Prior Art
In the operation of pressurized water power generating plants, it is desireable to have a system which will enable the early detection of failure of primary system mechanical components. The failure of such mechanical components characteristically results in metal debris which concentrate in the steam generator input plenum and the bottom plenum of the reactor vessel. Moreover, metal debris in the form of objects left in the system during the construction phase are sometimes encountered. Such metal debris, when left undetected, have caused extensive damage to various components of the coolant system.
During normal operation of the reactor system, the metal debris are transported to collection points by the normal flow of the primary coolant and, during their travel, are propelled against the metal walls enclosing the primary system coolant paths. Accordingly, surveillance of the energy imparted to the metal walls as a result of the impacts will provide both an indication of primary system component failure, and an indication of the presence of undesirable metallic debris which could cause subsequent failures.
To detect the presence of metallic debris in the nuclear reactor coolant system, various systems for detecting the impact energy have been utilized. One such system is disclosed, for example, in U.S. Pat. No. 3,860,481 issued Jan. 14th, 1975 to R. Gopal et al and assigned to Westinghouse Electric Corporation. According to this system, a number of impact sensors, e.g. accelerometers, are disposed at strategic positions on the nuclear reactor coolant system, e.g. at the reactor vessel upper and lower plenums and the input plenum of each steam generator of the reactor coolant system, and the output signals from the impact sensors are detected and analyzed. According to current regulations issued by the Nuclear Regulatory Commission, each impact sensor must have a sensitivity capable of detecting an impact energy of 0.5 foot-pounds (0.68 joules) within three feet (0.91 meters) of an impact sensor. Accordingly, in order to test the sensitivity of the impact sensors, it becomes necessary to periodically impart an external impact with an energy corresponding to the desired sensitivity to a surface of the reactor coolant system adjacent a particular impact sensor. Moreover, in order to stress the design limits of the various detection algorithms, researchers often desire to measure and control desired impact energies of even a smaller value than the required sensitivity for the system, e.g. less than 0.1 foot-pounds.
A number of methods and apparatus for imparting such external impact energies to a surface are known. Such devices may be, for example, a spring loaded mass which renders impact energy proportional to the spring constant, a pendulum device for providing an impact energy corresponding to the mass of the pendulum and the vertical height from which it is dropped to provide an impact, or a manually operated force hammer, including a transducer which produces an output which is a force versus time function, which is struck against the desired surface and the kinetic energy calculated from the area under the force versus time function.
All of the known devices suffer from the disadvantage that there is always a degree of uncertainty of the true impact energy. This results for example, because the first two devices include frictional forces and/or spring constants which may vary considerably, and because all of the devices involve some manual manipulation of the impact imparting device, thus rendering it difficult, to repeatedly apply an impact of a desired energy. Moreover, as a result of the manual manipulation involved, and the increased time required to determine or calculate the impact energy and, if necessary, vary the impact force and repeat the impact to provide the desired impact energy, the time of exposure to radiation by the personnel operating the impact device is undesirably increased. Finally, the known devices suffer from the problem that they are difficult, if not impossible, to use on surfaces with particular orientation or location. This latter problem is of particular significance when attempting to impact the bottom plenum of the reactor vessel which can only be approached from the bottom, and not from the side, and thus the impact must be applied in an upward vertical direction. This is not possible with a pendulum and difficult with the other devices.